1. Field of the Invention
The present invention relates to a method and apparatus for observing, before and after fusion-splicing of optical fibers such as ribbon fibers each including a plurality of optical fibers in particular, the butting state of the tip portion of each of fiber ribbons in a wide range with a high accuracy. Here, the fusion-splicing of the fiber ribbons is effected as optical fibers in one fiber ribbon are fusion-spliced with the respective optical fibers in the other fiber ribbon in a state where end faces of the corresponding optical fibers butt each other.
2. Related Background Art
As optical communication networks expand, high-density multifilament fiber-optic cables have been used, thereby necessitating a method for connecting them together with a low loss, a high reliability, and a rapidness. From this viewpoint, fusion-splicing machines for fiber ribbons (also known as ribbon type optical fibers) constituting the high-density multifilament fiber-optic cables have been developed. Here, "fiber ribbon" refers to a tape-shaped fiber cord in which a plurality of optical fibers are unitedly coated with a resin or the like. Also, each optical fiber comprises a core region having a predetermined refractive index and a cladding region which covers the outer periphery of the core region and has a lower refractive index than the core region.
FIG. 14 shows a configuration of the conventional fusion-splicing machine (including an observation apparatus) for fiber ribbons disclosed, for example, in U.S. Pat. No. 4,978,201. Fiber ribbons 1a and 1b to be spliced together are respectively held by fiber holding members 15a and 15b at their tip portions. The respective tip portions of the fiber ribbons 1a and 1b, stripped of coatings, are fixed onto installation members 16a and 16b, each having a plurality of V-shaped grooves. Disposed on both sides of the installation members 16a and 16b are electrodes 18a and 18b. After each of the butting tip portions of the fiber ribbons 1a and 1b is observed, the fiber ribbons 1a and 1b are fusion-spliced together by discharge between the electrodes 18a and 18b. A mirror 19, which is disposed between the electrodes 18a and 18b, is movable along directions indicated by arrow A in this drawing. A light source 5 and a microscope camera 20 are disposed such that irradiation light from the light source 5 is reflected by a mirror 19 and then is made incident on the microscope camera 20.
Further, the image data captured by the microscope camera 20 by way of the mirror is temporarily taken into an image processing unit 70. The image of the butting tip portions of the fiber ribbons 1a and 1b are displayed on a TV monitor 9 by the image processing unit 70.
Here, as shown in FIG. 15, after being reflected by the mirror 19, a part of the irradiation light from the light source 5 is transmitted through each optical fiber from the direction indicated by 23a so as to enter the microscope camera that has not yet been moved from its initial position 20a. On the other hand, a part of irradiation light from the moved light source 5 is transmitted through each optical fiber from the direction indicated by 23b in the drawing and then is reflected by the mirror 19 so as to enter the microscope camera that has been moved to a position denoted by 20b. In order to observe the butting state of the tip portions of the fiber ribbons 1a and 1b, the real images and virtual images of the tip portions of respective pairs of the optical fibers thus butting each other have been successively taken into the image processing unit 70 as image data while the microscope camera 20 is driven, or the real images and virtual images of the tip portions of a plurality of sets of optical fibers butting each other whose focal points do not considerably deviate from each other have been successively taken into the image processing unit 70 as image information.